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Abstract

We develop two algorithms for determining two inherent optical properties (IOPs) from radiometric measurements in vertically homogeneous waters. The first algorithm is for estimation of the ratio of the backscattering to absorption coefficients from measurements of only the vertically upward radiance and the downward planar irradiance at depths where the light field is in the asymptotic regime. The second algorithm enables estimation of the absorption coefficient from measurement of the diffuse attenuation coefficient in the asymptotic regime after use of the first algorithm. Multiplication of the two estimates leads to an estimate for the backscattering coefficient. The algorithms, based upon the use of a simplified phase function and the asymptotic eigenmode, are shown to potentially provide good starting conditions for iteratively determining the absorption and backscattering coefficients of a wide variety of waters. The uncertainty in the estimates defines a subspace for IOPs that may reduce ambiguity in such iterative solutions. Because of the ease of estimating the backscattering to absorption ratio from in-water measurements, this IOP deserves further investigation as a proxy for biogeochemical quantities in the open ocean.

Figures (5)

An IOP and a radiometric profile from the NAB08 dataset. (A) Typical IOPs were nearly homogeneous in the lit portion of the water column. (B) Radiometric profiles of Lu and Ed at 488 nm show little curvature until 40 m, another indication of vertically homogeneous water.

Estimates of F using rrs = Lu/Ed and IOP measurements from the NAB08 dataset. A) Values of fitted parameter F at 488 nm for all training set combinations (black x’s) and the linear fit for each value of k. Color indicates number of profiles k used in the training set. (B) fitted parameter F at selected wavelengths (color), created by linear fit for all k = 6 training set combinations.

Values of absorption a (A) and average error (B–C) at 488 nm, estimated from F, bb/a, ν0, and Kd (zas), using Eq. (41), and (D–F) estimated from bb/a and measurements of bb(470) and bb(700) using Eq. (44). Colors indicate the number of profiles k used to determine the value of F; remaining profiles are used to estimate bb/a, Kd (zas) and a.

Values of backscattering bb (A) and average error (B) and (C) at 488 nm, estimated from bb/a, F, and Kd (zas). Colors indicate the number of profiles k used to determine the value of F; remaining profiles are used to estimate bb/a, Kd (zas) and a.